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Introduction: Wetlands affect the levels of atmospheric carbon in two ways: First, many wetlands, particularly boreal and tropical peatlands, are carbon reservoirs. Carbon is contained in the standing crops of trees and other vegetation and in litter, peats, organic soils and sediments which have been built up, in some instances, over thousands of years. The magnitude of storage depends upon wetland type and size, vegetation, the depth of wetland soils, ground water levels, nutrient levels, pH and other factors discussed below. These carbon reservoirs may supply large amounts of carbon to the atmosphere if water levels are lowered or land management practices result in oxidation of soils. Second, many wetlands also continue to sequester carbon from the atmosphere through photosynthesis by wetland plants; many also act as sediment traps for carbon-rich sediments from watershed sources. However, wetlands also simultaneously release carbon as carbon dioxide, dissolved carbon, and methane. Deposited sediments are, in some instances, dislodged during floods and hurricanes. The net carbon sequestering versus carbon release roles of wetlands are complex and change over time although net, gradual sequestration occurs over time for peatlands and certain other types of wetlands. Land use practices also affect sequestering.